This invention relates to an engine start control apparatus for a hybrid vehicle which cranks an engine by using a motor which is for running, and which is provided in a drivetrain, as a starter motor, by engaging a normally-open hydraulic clutch provided between an engine and the motor.
U.S. Patent Application Publication No. 2003/0069104 A1 (corresponding to Japanese Patent Application Publication No. 2003-32808) discloses a conventional hybrid driving apparatus including a drivetrain including an engine, a motor, a normally-open hydraulic clutch disposed between the engine and the motor.
In this hybrid driving apparatus, when the engine is started in accordance with an engine start request after an ignition switch is switched to an ON state, operations are performed as follows.
(1) A motor is driven. A clutch hydraulic pressure generated based on a discharge pressure from an oil pump driven by the motor is ensured.
(2) The engine is cranked by using the motor as a starter motor while a hydraulic clutch is slip-engaged.
(3) The hydraulic clutch is fully engaged after the engine start is finished.
In the above-described process (1), the oil pump (for example, vane pump) has a generally well-known structure which sucks the hydraulic fluid stored in an oil pan through a strainer, and thereby generates the pump discharge pressure. When the pump discharge pressure is increased to a target hydraulic pressure, the clutch hydraulic pressure is ensured.